Polyesters and their manufacture from acids and glycol carbonates

ABSTRACT

Poly(ethylene terephthalate), poly(1,4-cyclohexanedicarboxylate), poly(ethylene isophthalate), poly(ethylene naphthalate), their copolymers with each other and with modifying aliphatic dicarboxylic acids, and substituted glycol repeat unit modifications thereof are produced from prepolymer (oligomer) obtained from the esterification of the acid or acids with ethylene carbonate or substituted ethylenecarbonate in the presence of one or more amines compounds selected from trialkylamines, tetraalkyldiamines, N-alkylated heterocyclic amines, and certain quaternary ammonium salts, employing certain mole ratios of ethylene carbonate and substituted ethylene carbonate to the diacid. The prepolymer is formed in an unusually short time and the final polyester of high I.V. exhibits improvement in such properties as desirable light color and low ether-glycol level.

This is a divisional of application Ser. No. 509,532 filed on June 30,1983, now U.S. Pat. No. 4,521,585 which is a continuation-in-partapplication of U.S. Ser. No. 405,795, filed Aug. 6, 1982, now abondoned,which is a continuation-in-part application of U.S. Ser. No. 291,609filed Aug. 10, 1981, now abandoned.

This invention concerns an improved process for the manufacture ofprepolymer, also known in the art as precondensate, oligomer or monomer,of inherent viscosities of from about 0.008 to about 0.20, preferably0.08 to 0.1, and the manufacture therefrom of polyesters such aspoly(ethyleneterephthalate),poly(ethylene-1,4-cyclohexanedicarboxylate), poly(ethyleneisophthalate),poly(ethylene-2,6-naphthalene dicarboxylate), their copolyesters, andmodifications thereof with aliphatic dicarboxylic acids, and suchpolyesters having alkyl or cyclohexyl substituted glycol repeat units,of molding, fiber forming or film forming inherent viscosity, i.e. fromabout 0.4 to about 1.2.

The prepolymer is obtained in accordance with the present invention fromthe esterification of one or more of terephthalic acid (TPA),1,4-cyclohexanedicarboxylic acid (CHDA), isophthalic acid (IPA), or anynaphthalenedicarboxylic acid (NDA), preferablynaphthalene-2,6-dicarboxylic acid, but including, e.g., 1,3-, 1,4-,2,5-, and 2,7- depicted by the general formula below, and up to about 50mole percent, preferably up to about 15 mole percent, based on totalmoles of acid reactant of an aliphatic dicarboxylic acid component(ADAC) consisting of one or a mixture of aliphatic dicarboxylic acids offrom 4 to 20 carbons (2-18 carbons in the hydrocarbon chain), withethylene carbonate (EC) or substituted ethylene carbonate (SEC), ormixtures thereof, in the presence of an amine component defined below.In the present process the mole ratio EC:TPA, EC:CHDA, and EC:NDA isfrom about 1 to about 2, preferably not exceeding about 1.8, and mostpreferably from 1.1 to 1.5, the mole ratio EC:IPA is from about 1 toabout 1.8, and preferably from 1.1 to 1.5, the mole ratio of EC:ADAC isfrom about 1 to about 2, preferably from 1.1 to 1.5, and the mole ratioof SEC to each of the diacids is from about 1.25 to about 3.0,preferably from 1.3 to 2.5. It is noted that when more than one acidand/or carbonate is employed, the mole ratios given above apply inproportion to the molar percentages of the acids and/or carbonatespresent to which the ratios apply, without regard to any apparent excessor deficiency of any particular acid or carbonate with respect to anyother reactant.

The final polymer (polycondensate) prepared according to the presentprocess exhibits improvements in color and/or reduction of theby-product ether-glycol level, for example, diethylene glycol (DEG) (theether-glycol being in reacted form in the polyester chain), and theadverse effects associated therewith. It is noted that the higherether-glycol levels typically lower the glass transition temperaturesand melting points of polyesters and adversely affects, for example,their gas and water vapor barrier properties, rendering them unsuitablefor certain packaging material applications. Also, in the presentprocess, the prepolymer can be made in a much shorter period of timethan possible, e.g., by the transesterification of dimethylterephthalate or dimethyl isophthalate with ethylene glycol (EG). Thepolyesters prepared from the present prepolymers are especially suitablefor use in fibers, beverage bottles, food packaging and the like.

In regard to one advantage of the present invention, publishedliterature preparations of polyesters from glycols containing twodifferently reactive hydroxyl functionalities such as 1,2-propanediolhaving one primary hydroxyl and one secondary hydroxyl, indicate thatthe overall reaction is a long and difficult one. For example,preparation of poly-(1,2-propyleneterephthalate) from dimethylterephthalate (DMT) and 1,2-propanediol is carried out at atmosphericpressure due to the low boiling point of 1,2-propanediol and an apparentlow reactivity. This transesterification process requires about twicethe time as the reaction of DMT with ethylene glycol. Moreover,presumably due to the majority of the free hydroxyl groups beingsecondary in the prepolymer, the polycondensation must be carried out atrelatively low temperatures of less than about 250° C. and preferablyabout 240° C. which results in very slow polycondensation. The use ofhigher temperatures for such polycondensations appears to causedehydration of a sufficient number of end groups to inactivate thepolymer segments after only a fraction of the desired molecular weightis attained. Likewise, preparation of such polymers from terephthalicacid has proven difficult because of low reactivity at the temperaturesrequired to avoid glycol distillation, and similarly, preparation fromdiacid chlorides suffers from expensive intermediates and solvent dryingrequirements for achieving satisfactorily high molecular weights.

In accordance with the present invention, we have discovered that theabove-mentioned preparation and final polymer problems may be overcomeby reacting the dicarboxylic acid with a cyclic ethylene carbonatehaving the formula ##STR1## wherein Z is hydrogen, cyclohexyl or alkyl,branched or straight, of 1-6 carbons, provided that the carbon attachedto the carbonate ring contains at least one hydrogen atom bound to it.Exemplary of such carbonates are propylene carbonate, 1,2-butylenecarbonate, 1,2-hexylene carbonate, cyclohexylethylene carbonate, andisopropylethylene carbonate. The alkyl carbonates may all be preparedfrom the corresponding 1,2-diols and a dialkyl carbonate such as diethylcarbonate, or from the epoxide and carbon dioxide. The preparation, forexample, of ethylene carbonate from ethylene oxide and CO₂ is describedin U.S. Pat. No. 4,117,250.

Many processing agents, including multivalent metals, trialkylamines,and certain quaternary ammonium halides are known in the prior art foruse in transesterifications or direct esterifications, but these agentsin general either do not give good color when applied to the reaction ofthe above acids and carbonates, are not taught for such reactions, orare not disclosed as having a catalytic effect thereon. See, forexample, U.S. Pat. Nos. 3,549,692 and 4,266,046; Ger. Offen. 1,952,094;JCS, Perkin 1977, pp 1266-71; and Japanese Pat. Nos. J 74 06,195 and J74 75,516.

We have found that the addition of an amine component selected from oneor more of trialkylamines, preferably triethylamine, tripropylamine andtributylamine, tetraalkyl nitrogen substituted diamines, N,N'-dialkylpiperazine, N-alkyl piperidine, and certain quaternary ammonium saltsdefined below, to the reaction mixture comprising one or more of TPA,IPA, CHDA, or NDA and EC and/or SEC results in unusually rapidprepolymer or oligomer formation and in improvements in the finalpolymer, i.e., inherent viscosities of above about 0.40 with, forexample in the EC reaction, DEG levels below about 1.0.

The trialkylamines useful herein have the formula R₃ N wherein the Ralkyl groups are all the same or mixed and are linear or branched of upto about 18 carbons. Preferred are those wherein each R is selected fromethyl, propyl and butyl, and most preferably each R is butyl. It isdesirable, in most cases, to employ trialkylamines having boiling pointsbelow the desired polycondensation temperature, i.e., below about280°-285° C. in order to recover said amines for recycle. The tetraalkylnitrogen substituted diamines have the formula R² R³ N-R¹ -NR⁴ R⁵wherein R¹ is straight or branched alkylene of 1-8 carbons, and each ofR², R³, R⁴ and R⁵ is independently selected from straight or branchedalkyl of 1-8 carbons. The alkyl moieties R² and R³ of the N,N'-dialkylpiperazine ##STR2## and the N-alkyl piperidine ##STR3## are as definedabove.

The quaternary ammonium salts (the term "salts", herein includescounterpart bases) useful herein have the general formula (R⁶)₄ N⁺ X⁻,wherein each R⁶ group is independently selected from linear or branchedalkyl of 1-18 carbons, and one of which may be benzyl, and wherein thecounterion X⁻ may be hydroxide or a carboxylate anion from a carboxylicacid such as acetic, propionic, benzoic, and the like. It is preferredthat each R⁶ group not exceed 8 carbons, and it is particularlypreferred that three of the R⁶ groups are methyl and the other is ahigher alkyl not exceeding 8 carbons, most preferably ethyl or butyl.Also particularly preferred is that each R⁶ is ethyl or butyl, and alsothat three R⁶ groups are ethyl and the remaining R⁶ is benzyl. Suchsalts generally give excellent color in the final polymer.

A preferred group of specific amine components comprises triethylamine,tripropylamine, tri-n-butylamine, ethyltrimethylammonium hydroxide,tetraethylammonium hydroxide, benzyltriethylammonium hydroxide,propyltrimethylammonium hydroxide, butyltrimethylammonium hydroxide,tetraethylammonium bromide, tetraethylammonium acetate,tetrabutylammonium hydroxide, and benzyltriethylammonium hydroxide.

Concentrations of the amine component as low as about 0.05 mole % basedon total EC or SEC moles generally provide a substantial rate increaseover the uncatalyzed reaction. Concentrations of these catalysts of upto about 5.0 mole % or higher based on total EC or SEC moles can also beused and show even larger rate increases although a diminishing effectis seen after a point. The preferred range for the trialkylamine andN-alkyl piperidine is 0.5 to 2.5 mole % for the ammonium salt is 0.25 to1.0 mole %, and for the tetraalkyldiamines and dialkyl piperazines is0.25 to 1.25 mole %.

As indicated above, another aspect of this invention involves theEC:TPA, EC:CHDA, EC:IPA, EC:NDA, and to a lesser extent, the EC:ADACmolar ratios used for the reaction. It has been found that the ratiosset forth above are suitable to give products having one or moredesirable properties such as light color, low ether-glycol, and highfinal polymer I.V. Ratios substantially above those limits usually willgive deeper color and higher ether-glycol levels even though theesterification reaction is considerably accelerated.

As aforesaid, in the polyester preparations, aliphatic dicarboxylicacids can be substituted for up to about 50 mole percent of the TPA,IPA, NDA, or CHDA to obtain certain desirable properties associated withsuch copolymers. Such aliphatic dicarboxylic acids include adipic,pimelic, suberic, azelaic, sebacic, and dodecanedioic acids or heteroatom containing diacids such as oxydiacetic acid. In general, forpackaging and similar applications, the mole percent modification bysuch diacids is preferably up to about 15 mole percent based on totalmoles of acid.

The esterification reaction giving the prepolymer having an I.V. of fromabout 0.008 to about 0.20 is carried out preferably in an inertatmosphere and at a temperature of from about 150° C. to about 265° C.,preferably 200° C. to 240° C., with the evolution of carbon dioxide. Thepreparation of the prepolymer is essentially complete when CO₂ evolutionceases as the result of complete reaction of the carbonate with thediacid. This prepolymer is a mixture of low molecular weight oligomerswhich have a statistical distribution of repeating units of the type,for example, in the case of TPA and EC, ##STR4## where n is usually notmore than two or three. The polycondensation reaction to build the I.V.to the desired level is then carried out by any of a wide variety ofknown processes such as at temperatures of from about 180° C. to about290° C., but usually preferably from about 240° C. to about 285° C.,under vacuum in the melt, or by solid state in a fixed-bed reactor as inU.S. Pat. No. 4,161,578 incorporated herein by reference, at atemperature of from about 200° C. to below the sticking point of thepolymer and in the presence of a suitable catalyst, e.g., titanium (asthe tetraisopropoxide) or antimony (as the triacetate) as a slurry inethylene glycol, in a concentration, for example, from about 50 to about400 ppm of Sb or 10-200 ppm of Ti based on the theoretical final polymerweight. The terms "sticking point" as used herein denotes temperatureswhich range from where the polymer particles just begin to tend to stickto each other to where sufficient sticking and agglomeration of theparticles occurs to seriously inhibit the necessary flow of polymer fromthe solid-stating reactor. The term "below" therefore, actually canencompass temperatures at which some sticking and agglomeration occurs,but which are still at an operable level.

In the esterification reaction, it is not necessary for the reactionmixture to become clear prior to raising the temperature required forpolycondensation, particularly if the mole ratio of carbonate to diacidis <2. It is, however, desirable in all cases for the melt to becomeclear for several minutes prior to beginning the polycondensation inorder to achieve greater clarity in the final polymer.

The prepolymer aspect of the present invention is defined as the processfor preparing prepolymer of an I.V. of from about 0.008 to about 0.20,having the same or different repeating units of the formula ##STR5## ormixtures thereof in any proportion, and wherein up to about 50 molepercent of A comprises the hydrocarbon chains of 2-18 carbons of one ormore aliphatic dicarboxylic acids of a modifying acid component (ADAC)consisting of one or a mixture of aliphatic dicarboxylic acids of 4-20carbons, and Z is H or a group selected from cyclohexyl and straight orbranched alkyl of 1-6 carbons, provided that the carbon of said Z groupwhich is attached to the main chain contains at least one hydrogen atombound to it, said process comprising reacting one or a mixture ofcarbonate reactants of the formula ##STR6## with one or a mixture ofterephthalic acid (TPA), 1,4-cyclohexanedicarboxylic acid (CHDA),isophthalic acid (IPA), or naphthalenedicarboxylic acid (NDA), and up toabout 50 mole percent of said aliphatic dicarboxylic acid component(ADAC), at a temperature of from about 150° C. to about 250° C., whereinthe mole ratio of the ethylene carbonate (EC) to TPA, CHDA, or NDA isfrom about 1 to about 2, the mole ratio of EC:IPA is from about 1 toabout 1.8, the mole ratio of EC:ADAC is from about 1 to about 2, and themole ratio of the substituted ethylene carbonate to each of the acids isfrom 1.25 to 3.0, and wherein the reaction is carried out in thepresence of from about 0.05 mole % to about 5.0 mole % based on totalmoles of carbonate reactant of an amine component selected from one or amixture of: trialkylamines having the formula R₃ N wherein each R is anindependently selected alkyl group, linear or branched of 1 to 18carbons; tetraalkyl nitrogen substituted diamines having the formula R²R³ N-R¹ -NR⁴ R⁵ wherein R¹ is straight or branched alkylene of 1-8carbons, and each of R², R³, R⁴ and R⁵ is independently selected fromstraight or branched alkyl of 1-8 carbons; ##STR7## wherein R² and R³are as defined above; and quaternary ammonium salts having the formula(R⁶)₄ N⁺ X⁻, wherein each R⁶ group is independently selected from linearor branched alkyl of 1-18 carbons, and one of which can be benzyl, andwherein X⁻ is hydroxide or a carboxylate anion.

The inherent viscosities (I.V.) of the prepolymer and polycondensate(final polymer) herein and in the examples below are determinedaccording to ASTM D2857-70 procedure, in a Wagner Viscometer of LabGlass, Inc. of Vineland, New Jersey, having a 1/2 ml. capillary bulb,using a polymer concentration of 0.5% by weight in 60/40 by weight ofphenol/tetrachloroethane. The procedure is carried out by heating thepolymer-solvent system at 120° C. for 15 minutes, cooling the melt to25° C. and measuring the time of flow at 25° C. The I.V. is calculatedfrom the equation ##EQU1## where:

{n}=inherent viscosity at 25° C. at a polymer concentration of 0.50g/100 ml. of solvent;

ln=natural logarithm;

t_(s) =sample flow time;

t_(o) =solvent-blank flow time; and

C=concentration of polymer in grams per 100 ml. of solvent=0.50.

The units of the inherent viscosity in all examples given below are indeciliters/gram.

The invention can be further understood by reference to the followingspecific examples which are not intended to limit the invention, butmerely to illustrate the same.

EXAMPLE 1

This example employs triethylamine to produce polyester of good colorand low DEG level.

In a flask fitted with stirrer, N₂ inlet, and a take-off for N₂ andvolatile products, were placed 83 g. (0.5 mol) of TPA, 88 g. (1.0 mol)of EC and 2.49 g. of Et₃ N. The mixture was stirred under N₂ with theflask placed in a molten metal bath at 200° C., and the temperaturegradually raised to 230° C. After 40 minutes, the melt had cleared andCO₂ evolution essentially ceased. The temperature of the metal bath wasthen raised to 280° C. and 250 ppm of Sb catalyst added as thetriacetate (calculated as Sb°). Vacuum was applied and the pressure heldat about 0.1 torr for 60 minutes after which the system wasrepressurized with nitrogen and the polymer allowed to cool andcrystallize. An I.V. of 0.59 was obtained and the polymer had a CDM+bcolor value of 3. Analysis by conventional hydrolysis/gas chromatographygave a DEG content of 0.46 wt. %.

EXAMPLE 2

This example employs tributylamine to produce a polyester having goodcolor and a low DEG level.

Into the apparatus of Example 1 were placed 83.0 g. (0.5 mol) of TPA, 66g. (0.75 mol) of EC and 2.49 g. of tributylamine. The conditions ofExample 1 were followed except that the esterification was allowed toproceed for about 70 min. An I.V. of 0.62 was obtained and the polymerhad a +b color value of 3.6. Analysis by hydrolysis/gas chromatographygave a DEG content of 0.58 wt. %.

EXAMPLE 3

This example illustrates the effect of various EC:TPA molar ratios,i.e., 2, 2.4 and 4.0, on the color and DEG levels of the resultantpolyester.

In three separate runs made according to Example 1, each using 41.5 g.of TPA (0.25 mol) and 0.2 g. of Et₃ N, EC was added in the followingamounts: (A) 44.0 g. (EC:TPA=2), (B) 52.5 g. (EC:TPA=2.4), and (C) 88.0g. (EC:TPA=4.0). The required esterification times were obtained byvisual determination of the time when the melts became clear. Thepolyesters were all analyzed by hydrolysis/gas chromatography for DEG,and the color inspected visually to give the results shown below:

    ______________________________________                                                Required                                                                      Esterification                                                        Sample  Time, Hr.    Wt. % DEG  Color                                         ______________________________________                                        (A)     3.0          0.95       Off-white                                     (B)     2.6          3.9        Tan                                           (C)     1.0          21.8       Dark brown                                    ______________________________________                                    

EXAMPLE 4

In this example using the conditions and apparatus of Example 1, 0.4 g.of sodium acetate was used as taught in Ger. Offen. 1,952,094. Theamounts of EC and TPA used for the reaction were twice those of sample(A) of Example 3 and the triethylamine was omitted. The melt did notbecome clear even after about five hours at 200° C. The final polymerhad a 0.57 I.V., a+b color value of 12.6 and contained 2.4 wt. % DEG.

EXAMPLE 5

This example compares the present invention with the use of imidazoleaccording to U.S. Pat. No. 3,549,692.

Test-tube size runs were made each using 4.98 g. of TPA and 5.28 g. ofEC. To one sample was added 0.15 g. of triethylamine (sample 1) and tothe other 0.0115 g. of imidazole (sample 2). The tubes were heated in aN₂ atmosphere at 220° C. and both samples were in solution in about 50minutes. Sample (2) had much more color (yellow-brown) than sample 1.After polymerizing as in Example 1 employing 250 ppm Sb added as theacetate, the color difference was much more pronounced in the polymers.

EXAMPLE 6

This example using the apparatus of Example 1 illustrates the use of aquaternary ammonium salt to produce polyester of good color and low DEG.

In the apparatus were placed 83.0 g. of TPA, 88.0 g. of EC and 0.29 g.of tetraethylammonium hydroxide (as a 25% by weight solution inmethanol). The whole was stirred under N₂ and placed in the molten metalbath at 200° C. After 80 minutes, the melt had cleared and CO₂ evolutionhad essentially ceased. The temperature of the metal bath was raised to285° C., 250 ppm Sb catalyst added (as the acetate) and vacuum appliedto a pressure of about 0.4 torr for 60 minutes to polycondense theproduct, after which the system was repressurized under N₂. The I.V. ofthe final polymer was 0.53 and had a+b color value of 4.0 and an Rdvalue of 84.0. The DEG level was determined by hydrolysis/gaschromatography to be 0.49 wt. %.

The above CDM +b color measurements (connoted+b) are obtained on aGardner Color Difference Meter, the Rd value being a measure of thelight reflectivity of the polymer, the higher the value the morereflectivity, and the +b value being a measure of the yellowness of thepolymer, the higher the value the deeper the yellow.

The following Examples 7-12 illustrate the EC/IPA aspect of the presentinvention. In these examples the times necessary for preparing theprepolymer were again obtained by visual observation of when the meltbecame clear. The apparatus employed in these examples was that used inExample 1.

Example 7 shows a superior polymer having a good I.V. and low DEGobtained by use of the present invention in preparing the prepolymer atrelatively low temperature and short reaction time.

Example 8 shows a conventional transesterification employing DMI and EGwhich takes a much longer time and higher temperature to prepare theprepolymer. The resulting final polymer, moreover, has excessively highDEG content.

Example 9 shows a conventional direct esterification with IPA and EGagain requiring longer times and higher temperatures. The resultingfinal polymer has excessively high DEG also.

Example 10 shows the same reaction as Example 9 but employing a muchhigher EG:IPA molar ratio in order to assist the esterification, andemploying the time-temperature profile of Example 7. The resultingpolymer had a slightly improved DEG level but a totally unacceptable lowI.V.

EXAMPLE 7

Into the flask were weighed 83.0 g (0.50 mol) of isophthalic acid, 52.8g (0.60 mol) of ethylene carbonate, and 5.55 g (0.03 mol) oftri-n-butylamine. The mixture was stirred under N₂ with the flaskimmersed in the metal bath held at 190° C. for 1 hr. and 45 min. Thetemperature of the bath was then raised to 280° C. and 0.6 ml of atitanium catalyst as acetyl trisopropyl titanate solution (1.76 wt. %Ti) in n-butanol was added. Vacuum was applied and the meltpolycondensed for 45 minutes at 0.15 torr. The metal bath was removed atthe end of this time and the apparatus repressurized with nitrogen andallowed to cool to solid polymer. The clear, yellow polymer had an I.V.of 0.806 and by hydrolysis/gas chromatography a DEG content of 0.41 wt.%.

EXAMPLE 8

The reactants were 97.0 g (0.5 mol) of dimethylisophthalate (DMI), 68.2g (1.1 mol) of ethylene glycol, and 0.6 ml of the titanium catalystsolution of Example 7. After stirring the mixture for 2 hrs. with theflask immersed in the metal bath held at 190° C., and then at 220° C.for 1 hour, the bath temperature was raised to 280° C. Upon reaching280° C., a vacuum was applied to the flask to achieve a pressure of 0.3torr. Polycondensation for 50 min. produced a light yellow polymer of0.849 I.V. which analyzed for 5.89 wt. % DEG.

EXAMPLE 9

The reactants were 83.0 g (0.50 mol) of isophthalic acid and 37.2 g(0.60 mol) of ethylene glycol. The mixture was stirred with the flaskheld in a 190° C. metal bath for four hours after which the bathtemperature was raised to 230° C. The melt became clear after about 50minutes at this temperature. The bath temperature was then raised to280° C., titanium catalyst added as in Example 7 and the meltpolycondensed for 45 minutes at a pressure of 0.1 torr. The resultingclear, yellow polymer had an I.V. of 0.787 and DEG content of 2.16 wt.%.

EXAMPLE 10

The catalyst and reactants for the esterification were the same as forExample 9 except that 68.2 g (1.1 mol) of ethylene glycol was used. Theresulting polymer after 45 minutes polycondensation at 280° C. and 0.1torr pressure had an I.V. of only 0.205 and contained 1.89 wt. % DEG.

EXAMPLE 11

This example illustrates that the use of tri-n-butylamine (Bu₃ N) isalone not sufficient when applied to the IPA-EG system of Example 9, toyield a combination of good I.V. and low DEG.

Parallel runs were made repeating Example 9 but with the second of theruns having 1.2 g of Bu₃ N added for the esterification. Using thetime-temperature profiles of Example 9, the resulting polymers analyzedas follows without Bu₃ N, I.V. was 0.791, and DEG was 1.93 wt. %; withBu₃ N, I.V. was 0.431, and DEG was 0.37 wt. %. Thus, although the DEGlevel was suppressed, the I.V. was unacceptably low, and the polymercolor with added Bu₃ N was dark.

EXAMPLE 12

This example illustrates the effect of increasing the mol ratio ofEC/IPA on color and DEG level employing the apparatus and reactionconditions of Example 1.

Reactions were run at the EC/IPA mol ratios of 2.0, 1.80, 1.5, and 1.2using 0.4 mol % Et₄ N⁺ Br⁻ as the catalyst for the esterification. Theresultant polymers were analyzed and tabulated as shown below:

    ______________________________________                                        Mol Ratio                                                                     EC/IPA    I.V.      DEG, Wt. % Color                                          ______________________________________                                        2.00      0.740     4.50       Dark Brown                                     1.80      0.670     0.81       Yellow                                         1.50      0.882     0.76       Yellow                                         1.20      0.864     0.69       Yellow                                         ______________________________________                                    

EXAMPLE 13A

This example illustrates the preparation of poly(1,2-propyleneterephthalate) by the method of this invention.

Terephthalic acid, 83.0 g. (0.5 mol), propylene carbonate, 153 g. (1.5mol), and Bu₃ N, 13.92 g. (0.075 mol) were combined in a 500-ml. singleneck round bottom flask fitted for volatiles removal, N₂ introduction,and with a stainless steel stirrer. The flask was immersed in a moltenmetal bath held at 220° C. After about 40 minutes the melt was clear.After 70 minutes, the bath was raised to 255° C., titaniumtetraisopropoxide catalyst added (about 100 ppm Ti by weight) and avacuum applied to a pressure of 0.2 torr. The polycondensation wascarried out for 110 minutes. The vacuum was then released and theproduct cooled under nitrogen. The clear polymer had an I.V. of 0.67, acarboxyl number of 29.7 eq/10⁶ g., and a Tg by DSC of 93° C.

EXAMPLE 13B

This example illustrates the preparation of the above polymer of 13A bythe previously known preferred method.

Dimethyl terephthalate, 97.0 g. (0.5 mol), propylene glycol, 114 g. (1.5mol) and enough titanium alkoxide and zinc acetate catalyst solutions toyield 100 ppm Ti by wt. and 130 ppm Zn by wt. in the final polymer werecombined in a flask fitted as described above. The metal bath was set at180° C. and held there for 2 hours, then raised to 190° C. for 2 hours,and then raised to 220° C. for 1 hour. The bath was then raised to 240°C. and the melt polycondensed by application of vacuum to a pressure of0.3 torr. After 90 minutes, the product had an I.V. of 0.39, a carboxylcontent of 35.5 eg/10⁶ g. of polymer, and a Tg of 93° C. (DSC).

EXAMPLE 14

This example illustrates the effects of differing mole ratios ofpropylene carbonate and reaction times on the polymers, showing that awide latitude is permissible.

In all cases, the terephthalic acid was used in the amount of 83.0 g.(0.5 mole). The propylene carbonate was ratioed to this and the Bu₃ Ncatalyst was held at 5 mol % of the carbonate present. The apparatus wasthat of Example 1.

    ______________________________________                                                Esterifi-                                                                     cation                                                                Carbonate/-                                                                           Time At  Time               Carboxyl                                                                             Tg,                                TPA     220° C.                                                                         in      Temp.,     no., 6 °C.                         Mole Ratio                                                                            in Min.  Min.    °C.                                                                          I.V. eq/10 g.                                                                             (DSC)                              ______________________________________                                        1.25    120      110     255   0.46 19.6   96                                 1.5     120       70     255   0.49 31.9   92                                 1.75    120       90     255   0.50 25.6   94                                 2.50     75      100     255   0.65 30.4   94                                 3.00     70      110     255   0.67 29.7   93                                 ______________________________________                                    

EXAMPLE 15

This example illustrates the preparation of poly (1,2-butyleneterephthalate). Terephthalic acid, 41.5 g. (0.25 mol), butylenecarbonate, 58.0 g. (0.50 mol) and Bu₃ N, 4.62 g. (0.025 mol) werecombined in a flask as an Example 1. After the mixture was stirred for 2hours at 225° C. bath temperature, the temperature was raised to 260°C., titanium tetraisopropoxide catalyst (100 ppm Ti by wt.) added andthe melt polycondensed for 1 hour 20 minutes at 0.1 torr pressure. Theclear polymer had an I.V. of 0.44.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. The process for preparing polyester of good color, aninherent viscosity (I.V.) of from about 0.4 to about 1.2 determinedaccording to ASTM D2857-70 procedure, in a Wagner Viscometer of LabGlass, Inc. of Vineland, New Jersey, having a 1/2 ml. capillary bulb,using a polymer concentration of 0.5% by weight in 60/40 by weight ofphenol/tetrachloroethane, and a reacted ether-glycol level of belowabout 1.0% by weight, comprising preparing prepolymer of an I.V. of fromabout 0.008 to about 0.20 having the same or different repeating unitsof the formula ##STR8## or mixture thereof in any proportion, andwherein up to about 50 mole percent of A comprises the hydrocarbonchains of 2-18 carbons of one or more aliphatic dicarboxylic acids of amodifying acid component (ADAC) consisting of one or a mixture ofaliphatic dicarboxylic acids of 4-20 carbons, and Z is H or a groupselected from cyclohexyl or straight or branched alkyl of 1-6 carbons,provided that the carbon of said Z group which is attached to the mainchain contains at least one hydrogen atom bound to it, by reacting oneor a mixture of compounds of the formula ##STR9## with one or a mixtureof terephthalic acid (TPA). 1,4-cyclohexanedicarboxylic acid (CHDA).isophthalic acid (IPA), or naphthalene dicarboxylic acid (NDA), and upto about 50 mole percent of said aliphatic dicarboxylic acid component(ADAC) at a temperature of from about 150° C. to about 250° C., whereinthe mole ratio of the ethylene carbonate (EC) to TPA, CHDA, or NDA isfrom about 1 to about 2 , the mole ratio EC:IPA is from about 1 to about1.8, the ratio EC:ADAC is from about 1 to about 2, and the mole ratio ofthe substituted ethylene carbonate to each of the acids is from 1.25 to3.0 and wherein the reaction is carried out in the presence of fromabout 0.05 mole % to about 5.0 mole % based on total moles of carbonatereactant of an amine component selected from one or more of:trialkylamines having the formula R₃ N wherein each R is anindependently selectd alkyl group, linear or branched of 1 to 18carbons: tetraalkyl nitrogen substituted diamines having the formula R²R³ N-R¹ -NR⁴ R⁵ wherein R¹ is straight or branched alkylene of 1-8carbons, and each of R², R³, R⁴ and R⁵ is independently selected fromstraight or branched alkyl of 1-8 carbons: ##STR10## wherein R² and R³are as defined above: quaternary ammonium salts having the formula (R⁶)₄N⁺ X⁻, wherein each R⁶ group is independently selected from linear orbranched alkyl of 1-8 carbons, or one of which is benzyl, and wherein X⁻is hydroxide or a carboxylate anion, and thereafter polycondensing saidprepolymer to produce said polyester.
 2. The process of claim 1 thepolycondensation is carried out in a stirred reactor at a temperature offrom about 200° C. to about 285° C., under a vacuum of from about 10 mmto about 0.1 Torr, in the presence of a catalyst comprising. from about50 to about 400 ppm of Sb, or from about 10 to about 200 ppm of Ti, ormixtures thereof.
 3. The process of claim 1 wherein the polycondensationis carried out in a solid state, fixed-bed reactor at a temperature offrom about 200° C. to below the sticking point of the polymer, in thepresence of a catalyst comprising from about 50 to about 400 ppm of Sb,or from about 10 to about 200 ppm of Ti, or mixtures thereof.